Motor neurons of adult animals, despite resistance to axotomy-induced cell death, undergo apoptotic cell death after nerve injury with removal of axon associated Schwann cells, indicating that neurotrophic factors from central glial cells may not be adequate to support the survival of injured neurons. This proposal aims to test the hypothesis that glial synthesis of neurotrophic factors can be up-regulated by steroid hormones, and that death of injured neurons is preventable by agents which scavenge free radicals and remove reactive oxygen species. Adult rat hypoglossal nerve innervating the tongue muscles will be lesioned on one side by crush (for reversible injury), ligation (to permanently disconnect neurons from target muscles but retain the proximal nerve segment), and avulsion (to deprive neurons of Schwann cell-derived neurotrophic factors). The vagus nerve will be crushed or transected to include parasympathetic motor neurons for comparison. Since progesterone (PG) and melatonin (MT) possess antioxidant activities; and in cerebral ischemia and truamatic injuries, reduce tissue damage, attenuate brain edema and cell loss, and facilitate functional recovery; and glial cells have PG receptors, nerve lesioned rats will receive PG injection daily via s.c. route, MT by osmotic pump infusion, combined treatment of the two agents, PG antagonist RU486 to block endogenous PG activities, and no treatment as control. Specific questions to be addressed are: (1) Will PG increase the synthesis of brain-derived neurotrophic factor (BDNF) and glial cell-line derived neurotrophic factor (GDNF)? (2) Will PG and MT prevent the loss of neurons after nerve avulsion? (3) What is the status of PG receptors in motor neurons before and after axotomy? Will PG affect the expression of PG receptors ininjured neurons? (4) Will a "death receptor" FAS be induced in neurons after nerve avulsion? Will PG and MT block the induction or reduce the expression of FAS and p75 in injured neurons? To answer these questions, tissue sections will be prepared for neuronal cell counting, and for immunostaining of BDNF, GDNF, PG receptors, FAS and p75, and quantify their levels by computerized image analysis. These studies will provide insight into the cellular and molecular events responsible for the initiation and activation of apoptotic pathways in injured neurons, and offer therapeutic potential for treating traumatic injuries and other neuropathological conditions.